We analyzed the function of ERF (ets-repressor-factor) gene by stable integration into a variety of cell lines. Clones of HeLa cells were very difficult to obtain (two out of hundreds of neo resistant clones), indicating that the overexpression of the ERF gene may be detrimental to the cell. In contrast, cell lines transformed by cytoplasmic oncogenes (mos, ras, src, met) were easily transformed by ERF and resulted in cell lines that exhibit reduced tumorigenicity either because of reduced levels of the transforming oncogene or by clocking downstream steps in the signal transduction pathway. We utilized the repressor domain of ERF gene to generate transcriptional repressors with altered DNA recognition sequences that could counteract endogenous transactivator. An ERGB/ERF fusion gene was capable of eliminating the transforming activity of the HTB86 cells which are derived from Ewing's sarcoma. Finally, a hybrid between the myc oncogene and the ERF repressor domain was constructed that exhibits repressor activity on myc-dependent promoter and we are currently testing its ability to reverse the transforming phenotype of Burkitt's lymphoma cells.